1. Field of the Invention
This invention discloses a new technique for determining the spin history of kinetic energy (KE) penetrator's. The method employs a special dihedral plug fitting into the rear (tracer well) of the KE penetrator to modulate a tracking radar's signal. This signal is recorded and analyzed to yield the rotation rate of the projectile as it flies down range. The dihedral plug has been tested with a Doppler range radar (HAWK AN/MPQ-33 X-band radar) but could also be exploited with non-Doppler radars provided enough output power is available.
2. Discussion of Prior Art
Knowledge of the spin history of kinetic energy (KE) penetrators (as for any projectile) is vital to designers in order to keep the spin frequencies below structural limits. Radar data have been used for measuring the spin of artillery projectiles where large features are present to produce modulated radar return signals from the rotation of the projectile.
The small size and features (see FIG. 1, section 6) of a KE penetrator provide for a meager radar cross section (RCS) and have prevented spin information from being extracted from the radar tracking data of these projectiles. Alternate techniques, such as using yaw cards which are described in Pennekamp, R. A., "Yaw and Spin Characteristics of the XM900E1 Model 545 APFSDS-T PROJECTILE," Ballistic Research Laboratory, APG, MD, BRL Report TR3846, June 1990. (AD B145808) have been used, but they are expensive, labor intensive, and can yield misleading results if the spin is atypical. Techniques employing high-speed framing cameras can be used, but only cover a small fraction of the projectile's flight.